Understanding and Mitigating Atomic Oxygen-Induced Degradation of Perovskite Solar Cells for Near-Earth Space Applications.

Combining high efficiency with good radiation tolerance, perovskite solar cells (PSCs) are promising candidates to upend expanding space photovoltaic (PV) technologies. Successful employment in a Near-Earth space environment, however, requires high resistance against atomic oxygen (AtOx). This work unravels AtOx-induced degradation mechanisms of PSCs with and without phenethylammonium iodide (PEAI) based 2D-passivation and investigates the applicability of ultrathin silicon oxide (SiO) encapsulation as AtOx barrier. AtOx exposure for 2 h degraded the average power conversion efficiency (PCE) of devices without barrier encapsulation by 40% and 43% (w/o and with 2D-PEAI-passivation) of their initial PCE. In contrast, devices with a SiO-barrier retained over 97% of initial PCE. To understand why 2D-PEAI passivated devices degrade faster than less efficient non-passivated devices, various opto-electrical and structural characterications are conducted. Together, these allowed to decouple different damage mechanisms. Notably, pseudo-J-V curves reveal unchanged high implied fill factors (pFF) of 86.4% and 86.2% in non-passivated and passivated devices, suggesting that degradation of the perovskite absorber itself is not dominating. Instead, inefficient charge extraction and mobile ions, due to a swiftly degrading PEAI interlayer are the primary causes of AtOx-induced device performance degradation in passivated devices, whereas a large ionic FF loss limits non-passivated devices.

Supramolecular Anchoring of Fe(III) Molecular Redox Catalysts into Graphitic Surfaces Via CH-π and π-π Interactions for CO2 Electroreduction.

Photoelectrochemical devices require solid anodes and cathodes for the easy assembling of the whole cell and thus redox catalysts need to be deposited on the electrodes. Typical catalyst deposition involves drop casting, spin coating, doctor blading or related techniques to generate modified electrodes where the active catalyst in contact with the electrolyte is only a very small fraction of the deposited mass. We have developed a methodology where the redox catalyst is deposited at the electrode based on supramolecular interactions, namely CH-π and π-π between the catalyst and the surface. This generates a very well-defined catalysts-surface structure and electroactivity, together with a very large catalytic response. This approach represents a new anchoring strategy that can be applied to catalytic redox reactions in heterogeneous phase and compared to traditional methods involves about 4-5 orders of magnitude less mass deposition to achieve comparable activity and with very well-behaved electroactivity and stability.

Biomimetic Photodegradation of Glyphosate in Carborane-Functionalized Nanoconfined Spaces.

The removal of organophosphorus (OP) herbicides from water has been studied using adsorptive removal, chemical oxidation, electrooxidation, enzymatic degradation, and photodegradation. The OP herbicide glyphosate (GP) is one of the most used herbicides worldwide, leading to excess GP in wastewater and soil. GP is commonly broken down in environmental conditions to compounds such as aminomethylphosphonic acid (AMPA) or sarcosine, with AMPA having a longer half-life and similar toxicity to GP. Metal-organic frameworks (MOFs) are excellent materials for purifying OP herbicides from water due to their ability to combine adsorption and photoactivity within one material. Herein, we report the use of a robust Zr-based MOF with a meta-carborane carboxylate ligand (mCB-MOF-2) to examine the adsorption and photodegradation of GP. The maximum adsorption capacity of mCB-MOF-2 for GP was determined to be 11.4 mmol/g. Non-covalent intermolecular forces between the carborane-based ligand and GP within the micropores of mCB-MOF-2 are thought to be responsible for strong binding affinity and capture of GP. After 24 h of irradiation with ultraviolet-visible (UV-vis) light, mCB-MOF-2 selectively converts 69% of GP to sarcosine and orthophosphate, following the C-P lyase enzymatic pathway and biomimetically photodegrading GP. Circumventing the production of AMPA is desirable, as it has a longer half-life and similar toxicity to GP. The exceptional adsorption capacity of GP by mCB-MOF-2 and its biomimetic photodegradation to non-toxic sarcosine make it a promising material for removing OP herbicides from water.

Metal Nanocatalyst Sintering Interrogated at Complementary Length Scales.

Metal nanoparticle (NP) sintering is a prime cause of catalyst degradation, limiting its economic lifetime and viability. To date, sintering phenomena are interrogated either at the bulk scale to probe averaged NP properties or at the level of individual NPs to visualize atomic motion. Yet, "mesoscale" strategies which bridge these worlds can chart NP populations at intermediate length scales but remain elusive due to characterization challenges. Here, a multi-pronged approach is developed to provide complementary information on Pt NP sintering covering multiple length scales. High-resolution scanning electron microscopy (HRSEM) and Monte Carlo simulation show that the size evolution of individual NPs depends on the number of coalescence events they undergo during their lifetime. In its turn, the probability of coalescence is strongly dependent on the NP's mesoscale environment, where local population heterogeneities generate NP-rich "hotspots" and NP-free zones during sintering. Surprisingly, advanced in situ synchrotron X-ray diffraction shows that not all NPs within the small NP sub-population are equally prone to sintering, depending on their crystallographic orientation on the support surface. The demonstrated approach shows that mesoscale heterogeneities in the NP population drive sintering and mitigation strategies demand their maximal elimination via advanced catalyst synthesis strategies.

Temperature-induced polymorphism of a benzothiophene derivative: reversibility and impact on the thin film morphology.

The identification of polymorphs in organic semiconductors allows for establishing structure-property relationships and gaining understanding of microscopic charge transport physics. Thin films of 2,7-bis(octyloxy)[1]benzothieno[3,2-b]-benzothiophene (C8O-BTBT-OC8) exhibit a substrate-induced phase (SIP) that differs from the bulk structure, with important implications for the electrical performance in organic field effect transistors (OFETs). Here we combine grazing incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM) to study how temperature affects the morphology and structure of C8O-BTBT-OC8 films grown by physical vapor deposition on SiO2. We report a structural transition for C8O-BTBT-OC8 films, from the SIP encountered at room temperature (RT) to a high temperature phase (HTP) when the films are annealed at a temperature T ≥ 90 °C. In this HTP structure, the molecules are packed with a tilt angle (≈39° respect to the surface normal) and an enlarged in-plane unit cell. Although the structural transition is reversible on cooling at RT, AFM reveals that molecular layers at the SiO2 interface can remain with the HTP structure, buried under the film ordered in the SIP. For annealing temperatures close to 150 °C, dewetting occurs leading to a more complex morphological and structural scenario upon cooling, with coexistence of different molecular tilts. Because the molecular packing at the interface has direct impact in the charge carrier mobility of OFETs, identifying the different polymorphs of a material in the thin film form and determining their stability at the interfaces are key factors for device optimization.

Trojans That Flip the Black Phase: Impurity-Driven Stabilization and Spontaneous Strain Suppression in γ-CsPbI3 Perovskite.

The technological progress and widespread adoption of all-organic CsPbI3 perovskite devices is hampered by its thermodynamic instability at room temperature. Because of its inherent tolerance toward deep trap formation, there has been no shortage to exploring which dopants can improve the phase stability. While the relative size of the dopant is important, an assessment of the literature suggests that its relative size and impact on crystal volume do not always reveal what will beneficially shift the phase transition temperature. In this perspective, we analyze the changes in crystal symmetry of CsPbI3 perovskite as it transforms from a thermodynamically stable high-temperature cubic (α) structure into its distorted low-temperature tetragonal (ß) and unstable orthorhombic (γ) perovskite structures. Quantified assessment of the symmetry-adapted strains which are introduced due to changes in temperature and composition show that the stability of γ-CsPbI3 is best rationalized from the point of view of crystal symmetry. In particular, improved thermal-phase stability is directly traced to the suppression of spontaneous strain formation and increased crystal symmetry at room temperature.

Surface-Promoted Evolution of Ru-bda Coordination Oligomers Boosts the Efficiency of Water Oxidation Molecular Anodes.

A new Ru oligomer of formula {[RuII(bda-κ-N2O2)(4,4'-bpy)]10(4,4'-bpy)}, 10 (bda is [2,2'-bipyridine]-6,6'-dicarboxylate and 4,4'-bpy is 4,4'-bipyridine), was synthesized and thoroughly characterized with spectroscopic, X-ray, and electrochemical techniques. This oligomer exhibits strong affinity for graphitic materials through CH-π interactions and thus easily anchors on multiwalled carbon nanotubes (CNT), generating the molecular hybrid material 10@CNT. The latter acts as a water oxidation catalyst and converts to a new species, 10'(H2O)2@CNT, during the electrochemical oxygen evolution process involving solvation and ligand reorganization facilitated by the interactions of molecular Ru catalyst and the surface. This heterogeneous system has been shown to be a powerful and robust molecular hybrid anode for electrocatalytic water oxidation into molecular oxygen, achieving current densities in the range of 200 mA/cm2 at pH 7 under an applied potential of 1.45 V vs NHE. The remarkable long-term stability of this hybrid material during turnover is rationalized based on the supramolecular interaction of the catalyst with the graphitic surface.

Improved thermal stability of antireflective moth-eye topography imprinted on PMMA/TiO2surface nanocomposites.

The thermal stability of antireflective moth-eye topographical features fabricated by nanoimprint lithography on poly (methyl methacrylate) (PMMA) incorporating TiO2nanoparticles is explored. The effect of nanoparticle load on the relaxation dynamics of the moth-eye nanostructure is evaluated via grazing incidence small angle x-ray scattering measurements byin situmonitoring the structural decay of the nanopatterns upon thermal annealing. It is demonstrated that the incorporation of TiO2nanoparticles to the imprinted surface nanocomposite films delays greatly the pattern relaxation which, in turn, enhances the stability of the patterned topography even at temperatures well above the polymer glass transition (Tg). The improved thermal behavior of the antireflective films will significantly enhance their functionality and performance in light-trapping applications where temperatures typically rise, such as solar devices or solar glass panels.

A Highly Water-Stable meta-Carborane-Based Copper Metal-Organic Framework for Efficient High-Temperature Butanol Separation.

Biofuels are considered sustainable and renewable alternatives to conventional fossil fuels. Biobutanol has recently emerged as an attractive option compared to bioethanol and biodiesel, but a significant challenge in its production lies in the separation stage. The current industrial process for the production of biobutanol includes the ABE (acetone-butanol-ethanol) fermentation process from biomass; the resulting fermentation broth has a butanol concentration of no more than 2 wt% (the rest is essentially water). Therefore, the development of a cost-effective process for separation of butanol from dilute aqueous solutions is highly desirable. The use of porous materials for the adsorptive separation of ABE mixtures is considered a highly promising route, as these materials can potentially have high affinities for alcohols and low affinities for water. To date, zeolites have been tested toward this separation, but their hydrophilic nature makes them highly incompetent for this application. The use of metal-organic frameworks (MOFs) is an apparent solution; however, their low hydrolytic stabilities hinder their implementation in this application. So far, a few nanoporous zeolitic imidazolate frameworks (ZIFs) have shown excellent potential for butanol separation due to their good hydrolytic and thermal stabilities. Herein, we present a novel, porous, and hydrophobic MOF based on copper ions and carborane-carboxylate ligands, mCB-MOF-1, for butanol recovery. mCB-MOF-1 exhibits excellent stability when immersed in organic solvents, water at 90 °C for at least two months, and acidic and basic aqueous solutions. We found that, like ZIF-8, mCB-MOF-1 is non-porous to water (type II isotherm), but it has higher affinity for ethanol, butanol, and acetone compared to ZIF-8, as suggested by the shape of the vapor isotherms at the crucial low-pressure region. This is reflected in the separation of a realistic ABE mixture in which mCB-MOF-1 recovers butanol more efficiently compared to ZIF-8 at 333 K.

Self-assembly of block copolymers under non-isothermal annealing conditions as revealed by grazing-incidence small-angle X-ray scattering.

An accurate knowledge of the parameters governing the kinetics of block copolymer self-assembly is crucial to model the time- and temperature-dependent evolution of pattern formation during annealing as well as to predict the most efficient conditions for the formation of defect-free patterns. Here, the self-assembly kinetics of a lamellar PS-b-PMMA block copolymer under both isothermal and non-isothermal annealing conditions are investigated by combining grazing-incidence small-angle X-ray scattering (GISAXS) experiments with a novel modelling methodology that accounts for the annealing history of the block copolymer film before it reaches the isothermal regime. Such a model allows conventional studies in isothermal annealing conditions to be extended to the more realistic case of non-isothermal annealing and prediction of the accuracy in the determination of the relevant parameters, namely the correlation length and the growth exponent, which define the kinetics of the self-assembly.

Study of the surface species during thermal and plasma-enhanced atomic layer deposition of titanium oxide films using in situ IR-spectroscopy and in vacuo X-ray photoelectron spectroscopy.

The thermal and plasma-enhanced atomic layer deposition (ALD) growth of titanium oxide using an alkylamine precursor - tetrakis(dimethylamino)titanium (TDMAT) - was investigated. The surface species present during both the precursor and co-reactant pulse were studied with in situ reflection mid-IR spectroscopy (FTIR) and in vacuo X-ray photoelectron spectroscopy (XPS). The thermal process using H2O vapor proceeds through a typical ligand exchange reaction mechanism. The plasma-enhanced ALD processes using H2O-plasma or O2-plasma exhibit an additional decomposition and combustion reaction mechanism. After the plasma exposure, imine (N[double bond, length as m-dash]C) and isocyanate (N[double bond, length as m-dash]C[double bond, length as m-dash]O) surface species were observed by in situ FTIR. In addition, nitrites (NOx) were detected using in vacuo XPS during the O2-plasma process. This study presents the importance of the use of in situ FTIR and in vacuo XPS as complementary techniques to learn more about the ALD reaction mechanism. While in situ FTIR is very sensitive to changes of chemical bonds at the surface, exact identification and quantification could only be done with the aid of in vacuo XPS.

Surface mobility and impact of precursor dosing during atomic layer deposition of platinum: in situ monitoring of nucleation and island growth.

The increasing interest in atomic layer deposition (ALD) of Pt for the controlled synthesis of supported nanoparticles for catalysis demands an in-depth understanding of the nucleation controlled growth behaviour. We present an in situ investigation of Pt ALD on planar Si substrates, with native SiO2, by means of X-ray fluorescence (XRF) and grazing incidence small-angle X-ray scattering (GISAXS), using a custom-built synchrotron-compatible high-vacuum ALD setup and focusing on the thermal Pt ALD process, comprising (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and O2 gas at 300 °C. The evolution in key scattering features provides insights into the growth kinetics of Pt deposits from small nuclei to isolated islands and coalesced worm-like structures. An analysis approach is introduced to extract dynamic information on the average real space parameters, such as Pt cluster shape, size, and spacing. The results indicate a nucleation stage, followed by a diffusion-mediated particle growth regime that is marked by a decrease in average areal density and the formation of laterally elongated Pt clusters. Growth of the Pt nanoparticles is thus not only governed by the adsorption of Pt precursor molecules from the gas-phase and subsequent combustion of the ligands, but is largely determined by adsorption of migrating Pt species on the surface and diffusion-driven particle coalescence. Moreover, the influence of the Pt precursor dose on the particle nucleation and growth is investigated. It is found that the precursor dose influences the deposition rate (number of Pt atoms per cycle), while the particle morphology for a specific Pt loading is independent of the precursor dose used in the ALD process. Our results prove that combining in situ GISAXS and XRF provides an excellent experimental strategy to obtain new fundamental insights about the role of deposition parameters on the morphology of Pt ALD depositions. This knowledge is vital to improve control over the Pt nucleation stage and enable efficient synthesis of supported nanocatalysts.

Formation and Functioning of Bimetallic Nanocatalysts: The Power of X-ray Probes.

Bimetallic nanocatalysts are key enablers of current chemical technologies, including car exhaust converters and fuel cells, and play a crucial role in industry to promote a wide range of chemical reactions. However, owing to significant characterization challenges, insights in the dynamic phenomena that shape and change the working state of the catalyst await further refinement. Herein, we discuss the atomic-scale processes leading to mono- and bimetallic nanoparticle formation and highlight the dynamics and kinetics of lifetime changes in bimetallic catalysts with showcase examples for Pt-based systems. We discuss how in situ and operando X-ray spectroscopy, scattering, and diffraction can be used as a complementary toolbox to interrogate the working principles of today's and tomorrow's bimetallic nanocatalysts.

Modeling collision energy transfer in APCI/CID mass spectra of PAHs using thermal-like post-collision internal energy distributions.

The internal energy transferred when projectile molecular ions of naphthalene collide with argon gas atoms was extracted from the APCI-CID (atmospheric-pressure chemical ionization collision-induced dissociation) mass spectra acquired as a function of collision energy. Ion abundances were calculated by microcanonical integration of the differential rate equations using the Rice-Ramsperger-Kassel-Marcus rate constants derived from a UB3LYP/6-311G+(3df,2p)//UB3LYP/6-31G(d) fragmentation mechanism and thermal-like vibrational energy distributions pME,Tchar. The mean vibrational energy excess of the ions was characterized by the parameter Tchar ("characteristic temperature"), determined by fitting the theoretical ion abundances to the experimental breakdown graph (a plot of relative abundances of the ions as a function of kinetic energy) of activated naphthalene ions. According to these results, the APCI ion source produces species below Tchar = 1457 K, corresponding to 3.26 eV above the vibrational ground state. Subsequent collisions heat the ions up further, giving rise to a sigmoid curve of Tchar as a function of Ecom (center-of-mass-frame kinetic energy). The differential internal energy absorption per kinetic energy unit (dEvib/dEcom) changes with Ecom according to a symmetric bell-shaped function with a maximum at 6.38 ± 0.32 eV (corresponding to 6.51 ± 0.27 eV of vibrational energy excess), and a half-height full width of 6.30 ± 1.15 eV. This function imposes restrictions on the amount of energy that can be transferred by collisions, such that a maximum is reached as kinetic energy is increased. This behavior suggests that the collisional energy transfer exhibits a pronounced increase around some specific value of energy. Finally, the model is tested against the CID mass spectra of anthracene and pyrene ions and the corresponding results are discussed.

Atomic layer deposited second-order nonlinear optical metamaterial for back-end integration with CMOS-compatible nanophotonic circuitry.

We report the fabrication of artificial unidimensional crystals exhibiting an effective bulk second-order nonlinearity. The crystals are created by cycling atomic layer deposition of three dielectric materials such that the resulting metamaterial is noncentrosymmetric in the direction of the deposition. Characterization of the structures by second-harmonic generation Maker-fringe measurements shows that the main component of their nonlinear susceptibility tensor is about 5 pm/V, which is comparable to well-established materials and more than an order of magnitude greater than reported for a similar crystal [Appl. Phys. Lett.107, 121903 (2015)APPLAB0003-695110.1063/1.4931492]. Our demonstration opens new possibilities for second-order nonlinear effects on CMOS-compatible nanophotonic platforms.

A complete map of the ion chemistry of the naphthalene radical cation? DFT and RRKM modeling of a complex potential energy surface.

The fragmentation mechanisms of the naphthalene molecular ion to [M-C4H2](+•), [M-C2H2](+•), [M-H2](+•), and [M-H(•)](+) were obtained at the UB3LYP/6-311+G(3df,2p)//UB3LYP/6-31G(d) level of theory and were subsequently used to calculate the microcanonical rate constants, k(E)'s, for all the steps by the Rice-Ramsperger-Kassel-Marcus formalism. The pre-equilibrium and steady state approximations were applied on different regions of the potential energy profiles to obtain the fragmentation k(E)'s and calculate the relative abundances of the ions as a function of energy. These results reproduce acceptably well the imaging photoelectron-photoion coincidence spectra of naphthalene, in the photon-energy range 14.0-18.8 eV that was previously reported by our group. Prior to dissociation, the molecular ion rapidly equilibrates with a set of isomers that includes the Z- and E-phenylvinylacetylene (PVA) radical cations. The naphthalene ion is the predominant isomer below 10 eV internal energy, with the other isomers remaining at steady state concentrations. Later on, new steady-state intermediates are formed, such as the azulene and 1-phenyl-butatriene radical cations. The naphthalene ion does not eject an H atom directly but eliminates an H2 molecule in a two-step fragmentation. H(•) loss occurs instead from the 1-phenyl-butatriene ion. The PVA ions initiate the ejection of diacetylene (C4H2) to yield the benzene radical cation. Acetylene elimination yields the pentalene cation at low energies (where it can account for 45.9%-100.0% of the rate constant of this channel), in a three-step mechanism starting from the azulene ion. However, above 7.6 eV, the major [M-C2H2](+•) structure is the phenylacetylene cation.

In Situ Annealing Effect on Thermally Co-Evaporated CsPbI2Br Thin Films Studied via Spectroscopic Ellipsometry.

All-inorganic cesium lead halide perovskites possess excellent thermal stability, a feature that renders them highly favorable for optoelectronic applications with an elevated thermal budget. Employing a coevaporation approach for their deposition holds promise for manufacturing at an industrial level, owing to improvements in device scalability and reproducibility. For unlocking the full potential of vacuum-evaporated perovskite thin films, it is crucial to delve deeper into their crystallization process, which, as a solid-state reaction, has been less investigated compared to the crystallization process of, most commonly used, solution-based methods. In this work, we employ spectroscopic ellipsometry, a nondestructive, high speed, and high accuracy characterization method, to study the real time annealing effect on thermally coevaporated CsPbI2Br thin films in a temperature range between 25 and 300 °C. We achieve this by developing a singular dynamic model that can be fitted in real time as a function of temperature, providing insights into how thermal annealing influences the perovskite film's morphology and optical constants. Based on the latter, we derive the temperature dependence of the thermo-optic coefficient and Urbach energy as well as analyze the interband transition energies via critical point analysis. We demonstrate that the γ- to ß-phase transition can be identified through a pronounced shift in the bandgap energy, whereas the ß- to α-phase transition can be discerned by a sharp increase in the film's roughness. We corroborate the obtained fit results with additional in- and ex situ measurements, such as in situ grazing incidence wide-angle X-ray scattering, atomic force microscopy, reflectance/transmittance, and profilometry.

Controlling Pt nanoparticle sintering by sub-monolayer MgO ALD thin films.

Metal nanoparticle (NP) sintering is a major cause of catalyst deactivation, as NP growth reduces the surface area available for reaction. A promising route to halt sintering is to deposit a protective overcoat on the catalyst surface, followed by annealing to generate overlayer porosity for gas transport to the NPs. Yet, such a combined deposition-annealing approach lacks structural control over the cracked protection layer and the number of NP surface atoms available for reaction. Herein, we exploit the tailoring capabilities of atomic layer deposition (ALD) to deposit MgO overcoats on archetypal Pt NP catalysts with thicknesses ranging from sub-monolayers to nm-range thin films. Two different ALD processes are studied for the growth of MgO overcoats on Pt NPs anchored on a SiO2 support, using Mg(EtCp)2 and H2O, and Mg(TMHD)2 and O3, respectively. Spectroscopic ellipsometry and X-ray photoelectron spectroscopy measurements reveal significant growth on both SiO2 and Pt for the former process, while the latter exhibits a drastically lower growth per cycle with an initial chemical selectivity towards Pt. These differences in MgO growth characteristics have implications for the availability of uncoated Pt surface atoms at different stages of the ALD process, as probed by low energy ion scattering, and for the sintering behavior during O2 annealing, as monitored in situ with grazing incidence small angle X-ray scattering (in situ GISAXS). The Mg(TMHD)2-O3 ALD process enables exquisite coverage control allowing a balance between physically blocking the Pt surface to prevent sintering and keeping Pt surface atoms free for reaction. This approach avoids the need for post-annealing, hence also safeguarding the structural integrity of the as-deposited overcoat.

Solution-Processed Pb(Zr,Ti)O3 Thin Films with Strong Remnant Pockels Coefficient.

In contrast to the widely studied electrical properties of Pb(Zr,Ti)O3 thin films, which have led to their applicability in various application areas such as thin film capacitors, microelectronics, and ferroelectric memories, the electro-optic (EO) properties are far less studied, which hinders the applicability of Pb(Zr,Ti)O3 films for EO applications such as heterogeneously integrated phase modulators in silicon (Si) photonics. Therefore, the EO properties of Pb(Zr,Ti)O3 films need to be further investigated to pave the way for the applicability of Pb(Zr,Ti)O3 films in EO applications. As the EO properties of ferroelectric thin films strongly depend on their crystal phase and texture, which in turn are influenced by the method of film fabrication. Therefore, in this work, we investigate the EO properties of a promising solution process using a La2O2CO3 template film. We successively characterize the precursor ink, microstructure and EO properties of the solution-processed Pb(Zr,Ti)O3film. The Pb(Zr,Ti)O3 film exhibits a fiber texture and has a large maximum and remnant Pockels coefficient (reff) of 69 pm V-1 and 66 pm V-1, respectively. The integration into a ring resonator-based modulator shows a VπL of 2.019 V cm. The determination of these promising EO properties could further pave the way for the applicability of Pb(Zr,Ti)O3 thin films in Si photonics.

Oxygen-Mediated (0D) Cs4PbX6 Formation during Open-Air Thermal Processing Improves Inorganic Perovskite Solar Cell Performance.

The desire to commercialize perovskite solar cells continues to mount, motivating the development of scalable production. Evaluations of the impact of open-air processing have revealed a variety of physical changes in the fabricated devices─with few changes having the capacity to be functionalized. Here, we highlight the beneficial role of ambient oxygen during the open-air thermal processing of metastable γ-CsPbI3-based perovskite thin films and devices. Physiochemical-sensitive probes elucidate oxygen intercalation and the formation of Pb-O bonds in the CsPbI3 crystal, entering via iodine vacancies at the surface, creating superoxide (O2-) through electron transfer reactions with molecular oxygen, which drives the formation of a zero-dimensional Cs4PbI6 capping layer during annealing (>330 °C). The chemical conversion permanently alters the film structure, helping to shield the subsurface perovskite from moisture and introduces lattice anchoring sites, stabilizing otherwise unstable γ-CsPbI3 films. This functional modification is demonstrated in γ-CsPbI2Br perovskite solar cells, boosting the operational stability and photoconversion efficiency of champion devices from 12.7 to 15.4% when annealed in dry air. Such findings prompt a reconsideration of glovebox-based perovskite solar cell research and establish a scenario where device fabrication can in fact greatly benefit from ambient oxygen.